Inside View: February 2008

January 30, 2008
Written by Gary Jones
Bio-fungi potential: promising new products.
Exciting developments are occurring in the realm of beneficial fungi. A recent Institute for Sustainable Horticulture seminar in British Columbia highlighted potential fungal allies.

Metarhizium anisopliae in Root Weevil Management (Dr. Denny Bruck, USDA, Horticultural Crops Research Laboratory, Oregon) – Nursery and greenhouse ornamental growers know root weevils! Chemical insecticides can be successful but may result in secondary pest outbreaks, limited crop re-entry, or potential environmental harm. Registration for the fungus Metarhizium anisopliae (‘Met52’) is expected in Canada this year. Spores require contact with weevil larvae, so they must either be incorporated into the growing media or drenched. M. anisopliae incorporated into a peat/bark medium at potting killed 96-100 per cent of final instar black vine weevil, and in large-scale field trials persisted for up to two growing seasons at concentrations sufficient for significant weevil control. With container media temperature above 16º C (60ºF), drench applications effectively eliminated black vine weevil larvae. However, M. anisopliae as a curative drench has similar temperature-dependent limitations to nematode applications.

Controlling root diseases with biocontrol fungi – mechanisms of action (Dr. Zamir Punja, Simon Fraser University, B.C.)  – The biocontrol product ‘Prestop Mix’ (Gliocladium catenulatum [G.c.]) provides effective control of Fusarium and Pythium root rot on cucumber. Roots, especially tips, are extensively colonized by G.c. seven days after application at seeding, and survived for up to 50 days. Hyphae were present in underlying epidermal cells of roots and stems, suggesting endophytic (“in the plant”) colonization. Extensive root colonization and hydrolytic enzyme production appear to contribute to the efficacy of G. catenulatum.

Influence of Root and Endophytic Associations on Success of Entomopathogenic Fungal Infection (Dr. Denny Bruck) – Applying large amounts of inoculum of entomopathogenic fungi to protect plants from insect feeding presents numerous problems. Techniques using either endophytic or root zone-compatible isolates of such fungi may benefit application costs and logistics. Beauveria bassiana and Metarhizium anisopliae have been successfully used in these ways. When selecting entomopathogenic fungal isolates, understanding factors associated with biology outside of the insect host appears more important than virulence in laboratory bioassays.

Microbial control of greenhouse mites in Britain. (Dr. David Chandler, University of Warwick/Horticulture Research International, UK.) – Mite control on protected crops is most effective when including a fast-acting microbial control agent to replace chemical acaricides currently used. Spider mites, with sucking/piercing mouthparts, are unlikely to acquire microbial control agents by ingestion. The best option is a fungus with contact activity.

Grower-levy funded lab bioassays measured susceptibility of T. urticae to infection by entomopathogenic fungi on
tomato. Effective isolates include L. muscarium 19.79 and Beauvaria bassiana 432.99, proprietary biopesticides ‘Mycotal’ and ‘Naturalis-L’.

Five entomopathogenic fungi (spray applications) significantly reduced mite populations on mature tomato. B. bassiana was most effective, reducing mite numbers by 97 per cent on upper leaves. ‘Naturalis-L’ was a very effective remedial treatment, outperforming fenbutatin oxide sprays. However, Chandler suspects lower mite numbers were caused by less spider mite prey in the treatments, causing mite migration, rather than the products giving effective kill.

Work comparing effects of four entomopathogenic fungi on two-spotted spider mite and carmine spider mite (causing hyper-necrosis), showed no significant difference in susceptibilities of these two mites to the four fungi, indicating bioassays done on one mite strain may be extrapolated to others.

U.S. researchers have reported reduced effects of entomo-pathogenic fungi on insects feeding on tomatoes compared to cucumber. Chandler’s work, however, indicated that tomato variety and type had relatively little effect on fungal infectivity.

Fighting insects and diseases; can fungi play a dual role? (Dr. Mark Goettel, Agriculture and Agri-food Canada, Lethbridge.) –  Biopesticides based on entomopathogenic fungi are commercially available for use against greenhouse pests. Other fungi are antagonistic to plant pathogens and are marketed for disease management. However, entomopathogenic fungi may have potential for dual management of invertebrate pests and plant pathogens. Dr. Goettel showed three species of Lecanicillium had significant effects on both aphids and cucumber powdery mildew.

Also covered were “Microbial control of Western Flower Thrips” and “Microbial Control of Glasshouse and Field Diseases in Britain” (e.g., controlling Sclerotinia with Coniothyrium) and work on Trichoderma.

DVD proceedings from this and other ISH conferences will soon be available ( www.kwantlen.ca/ish).n

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